1. Field of the Invention
This invention relates to a method of controlling individual cylinder fuel injection quantities in an electronically controlled diesel engine and a device therefor, and particularly to improvements in a method of controlling individual cylinder fuel injection quantities in an electronically controlled diesel engine and a device therefor, suitable for use in an electronically controlled diesel engine in a motor vehicle, wherein rpm variations with every explosion cylinder are detected and compared with one another, and a fuel injection quantity control actuator is controlled with every cylinder so as to make the rpm variations of respective cylinders uniform, so that engine vibrations due to a dispersion in fuel injection quantity between the cylinders can be reduced.
2. Description of the Prior Art
In general, the vibrations of a diesel engine during idling are by far higher than those of a gasoline engine. The diesel engine resiliently supported by an engine mounting mechanism resonates with the engine vibrations, resulting in not only worsening the comfortableness of a vehicle, but also adversely affecting components around the engine. This is mainly caused by the vibrations of the primary/secondary low frequencies attributed to periodical dispersions of the fuel fed under pressure to the respective cylinders at a cycle only half the turn of the diesel engine when the diesel engine is of four cycle type for example. More specifically, in a diesel engine, if a dispersion occurs in the fuel injection quantity between the cylinders, then, as shown in FIG. 1, the rpm variations .DELTA.NE between the explosion cylinders (in the case of the engine of four cylinders, 180.degree.CA (crank angle)) are not equal to one another, whereby surging S of deviations about a crank occurs at a cycle of every four explosions, which surge gives an uncomfortable feeling to an occupant of a vehicle. In the drawing, designated at TDC is a top dead center.
For this, it is conceivable that an engine body, a fuel injection pump and an injection nozzle are manufactured with very high accuracies, so that a dispersion in fuel quantities fed to respective cylinders can be reduced. However, to achieve this, great difficulties in production engineering are encountered, and a fuel injection pump and the like become very expensive. On the other hand, it is also conceivable that an engine mounting mechanism is improved so as to reduce the vibrations of the engine. However, the mounting mechanism becomes complicated and expensive, and further, the vibrations of the diesel engine itself are not reduced thereby, thus not enabling to offer the fundamental solution of the problem.
To obviate the above-described problem, it is conceivable that an NE raw wave form is obtained by a gear 20 secured to a drive shaft 14 of a fuel injection pump 12 and an engine rotation sensor 22 mounted to a pump housing 12A as shown in FIG. 2 for example, an engine speed NEi(i=1 to 4) through a rotation of 45.degree.CA immediately before the cylinder to be corrected is calculated from the time duration .DELTA.T needed for the rotation through 45.degree.CA, i.e. the rotation through 22.5.degree.PA (pump angle) (45.degree.CA of the engine) of the drive shaft 14 for example, which is detected by a fall of an NE pulse having formed the NE raw wave form as shown in FIG. 3, an rpm variation DNE.sub.p (p=1 to 4) with every explosion cylinder is detected from the engine speed NEi as shown in FIG. 4, the resultant value is compared with a mean value (hereinafter referred to as a "mean rpm variation") ##EQU1## of the rpm variations of all of the cylinders, when the rpm variation of the cylinder is smaller than the mean rpm variation WNDLT, the fuel injection quantity of the cylinder is regarded to be small, a fuel injection quantity (hereinafter referred to as an "everytime correction quantity") .DELTA.q to be increased is learned in accordance with a difference (hereinafter referred to as an "rpm variations difference") DDNE.sub.p (p=1 to 4), as shown in FIG. 5 for example, and reflected at the time of a subsequent fuel injection of the cylinder. On the contrary, when the rpm variation of the cylinder is larger than the mean rpm variation WNDLT, to decrease the fuel injection quantity of the cylinder. A fuel injection control actuator, such for example as a spill actuator for controlling a spill ring in a distribution type fuel injection pump is controlled with every cylinder until the rpm variations of the respective cylinders become uniform as illustrated in FIG. 6 for example, whereby the fuel injection quantity is increased or decreased with every cylinder, so that the dispersion in fuel injection quantity between the cylinders can be obviated, thereby enabling to reduce the engine vibrations.
Referring to FIG. 6, .DELTA.Q.sub.p (p=1 to 4) is an individual cylinder correction quantity as being an integrated value of the everytime correction quantities .DELTA.q, K.sub.5 is a coefficient of correction for preventing hunting when the engine speed is within a range between 1000 rpm and 1500 rpm during neutral position, wherein the higher the engine speed is, the lower the individual cylinder correction quantity is made, Q.sub.fin is an injection quantity calculated from a mean engine speed NE, an accelerator opening Accp and the like, and Vsp is an output from a spill position sensor for detecting a displacement of the spill actuator.
However, since the upper and lower guard limit values of the individual cylinder correction quantity .DELTA.Qp have heretofore been set at constant values, but not determined by the temperature, in some cases, the movement of the spill ring has not reached the individual cylinder correction quantity .DELTA.Qp by the injection time as shown in FIG. 7, because the follow-up action of the spill ring becomes slow at the time of low temperature where the fuel viscosity becomes high, such for example as at the fuel temperature of -20.degree. C. or less. Then, since the individual cylinder correction quantity .DELTA.Qp is not satisfactorily corrected, such a vicious circle arises that a deviation of the rpm variation DDNEp ( =WNDLT-DNEp ) is not decreased and an everytime correction quantity .DELTA.q of the succeeding time corresponding to the deviation of rpm variation DDNEp is further integrated to the individual cylinder correction quantity .DELTA.Qp, is diverged to the upper and lower limit values, exceeding a range, which the spill ring can follow up, as shown in FIG. 8 (an example of the coolant temperature of -20.degree. C. or less), the individual cylinder correction quantity .DELTA.Qp and the spill ring movement do not correspond to each other so that the individual cylinder injection quantity correction cannot be made in time, and the correction of the succeeding cylinder is interfered with, thus presenting such a disadvantage that the individual cylinder correction cannot be made satisfactorily.